This invention relates to a novel process for the oxidation of secondary and tertiary alkylaromatic hydrocarbons such as cumene, ethylbenzene, sec.-butylnaphthalene and the like to form the corresponding oxidation products, such as alcohols, aldehydes, ketones, hydroperoxides, and the like. The invention also relates to certain novel organometallic complexes useful as oxidation catalysts in this process. More particularly, this invention is directed to the use of complexes formed by reacting metal salts with a hexaalkylphosphoramide (hereinafter HAPA) as oxidation catalysts in the aforesaid process, and especially those complexes formed between HAPA and lanthanide metal salts.
The oxidation of the alkyl side chains of aromatic compounds is already well known in the art. Thus, for example, it is known that tertiary alkylaromatics such as cumene can be auto-oxidized very slowly to form cumyl hydroperoxide when air or oxygen is rapidly passed through cumene warmed to about 80.degree. C. Also, Canadian Pat. No. 510,517 teaches that the rate of oxidation of cumene can be enhanced when carried out in the presence of alkali or alkaline earth metal oxides of hydroxides, or in the presence of salts and oxides of heavy metals. Under these conditions, the conversion rate is only 2-3 percent per hour. Other alkylaromatic oxidation catalysts are likewise well known, but in most instances, again, the conversion rate is low, as is the overall yield of the desired oxidation product.
It is an object of this invention, therefore, to provide a novel process for the oxidation of secondary and tertiary alkylaromatic compounds whereby the oxidation rate, or the selectivity, or both, may be increased, particularly with respect to the formation of the corresponding hydroperoxides.
It is a further object of this invention to provide certain novel organometallic complexes useful as catalysts in the oxidation process.